Wednesday, January 25, 2012

New USDA Zone Map Unveiled

Today the U.S. Department of Agriculture (USDA)  released the new version of its Plant Hardiness Zone Map (PHZM), updating this useful tool for gardeners for the first time since 1990 with greater accuracy and detail. The new map was jointly developed by USDA's Agricultural Research Service (ARS) and Oregon State University's (OSU) PRISM Climate Group and is available online at

Plant hardiness zone designations represent the average annual extreme minimum temperatures at a given location during a particular time period. They do not reflect the coldest it has ever been or ever will be at a specific location, but simply the average lowest winter temperature for the location over a specified time. Low temperature during the winter is a crucial factor in the survival of plants at specific locations. It allows us to catalog shop or go to the nurseries and find with some accuracy what plants will survive in our gardens and which ones will not.

For the first time the map is "Internet friendly". There is a terrific feature where you can plug in your zip code and it will automatically give you your zone and the average minimum temperature range. My garden is now in Zone 8B with a low temperature range of 15-20 F. Many gardeners will find that they are now gardening in an area one half-zone warmer than before.

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